Communication exchange system



SePt- 3,1942 G. DEA-K1N l n y .N 2,2955032 COMMUNICATION EXCHANGE lSYSTEM lNyEN'ToR Byh E11 I Q ATTORNEY COMMUNICATION EXCHANGE SYSTEM Filed July 24, 1959 2 sheets-sheet :al

y I l -I* MV I I JAnAA Q FIG. .2.

W/PFRS W FIG. l3.

ATTORNEY v Patented Sept. 8, 1942 UNITED STAT S wenn COMMUNICATION EXCHANGE SYSTEM Application July 24, 1939, Serial No. 286,220

14 Claims.

The present invention relates to telephone or the like central exchange systems and especially to such systems of the central battery automatic or semi-automatic type.

It is an object of the present invention to provide such an exchange system wherein the individual line equipments shall be greatly reduced in cost and complexity, thus decreasing both the initial cost and the maintenance of such equipments. It is a further object of the invention to provide such an exchange system having a large number of lines, a. smaller number of line finder equipments each common to a group of lines, and a still smaller number of equipments common to a number of line nders and serving to perform the functions ordinarily performed by the line and cuto relays individual to each line.

In particular it is an object of the present invention to provide such an exchange system wherein the functions ordinarily performed by the line and cutoff relays individual to each line are instead performed by equipment common to lll a number of lines and wherein the amount of electron discharge means capable of being actuated through resistanoes Very large in comparison with the talking circuit impedances whereby potentials for actuating such electron discharge means may be permanently applied to the line through very high resistances and may be left connected to the line during talking without impairing the transmission characteristics of the line. It is a further object to provide such electron discharge means which shall be substantiali ly instantaneously responsive to momentary connection of signalling potentials whereby one such means may be very rapidly successively connected to a large number of lines or groups of lines for detecting the presence of a calling condition on any of said lines.

The exact nature of the invention may best be understood from the following description taken in conjunction with the attached drawings, in which Fig. l represents schematically a portion of an exchange embodying the invention;

Fig. 2 illustrates schematically a modified multipling arrangement which may be substituted in the system of Fig. 1;

Fig. 3 represents a combinedv starting and testing arrangement which may be substituted in the system of Fig. 1 whether this system be unmodified as shown in Fig. 1, or modified by the substitution therein of the modifying arrangement of Fig. 2.

Referring more particularly to Fig. 1, H, H represent the hook switches of anumber of subscribers telephone sets which are respectively connected to the several lines a-ba In the central exchange each of these lines 2t-br has connected to it a number of simple ohmic resistors J, K, L. The L resistor which may be of the order of 50,000 ohms is permanently connected to the b wire of each line and its free end is connected to the negative pole of the exchange battery whose positive terminal is grounded in conventional fashion. The K resistor associated with each line is preferably equal in resistance to the L resistor and is connected at its free end to the common start wire lc preferably through the individual line resistor J. The two wires a, b of each line are further multipled to the terminals of a number of line nders as indicated in the drawings, only two such line 'finders I and II being shown although it will be understood that ordinarily a larger number will be provided. These line finders are shown as linear motion switches for convenience of illustration, but are preferably single motion rotary 'switches of step by step or power driven type. The a and b wires are also multipled to connector terminals (not shown) in similar fashion.

Within the exchange a third or c wire is also associated with each line as is usual in common battery exchanges and this third or c wire is likewise multipled along with the a and b wires to the terminals of the line ndersas shown (and also similarly to the terminals of connectors not shown), each c wire being also connected to the junction between the J and K resistors individual to the line under consideration.

It will thus be seen that the connection arrangement differs from that generally used principally in the fact that the b side of each line is connected to battery through a high resistance L, while the a side of each line is connected through a high resistance K to the associated c wire, these c wires being then all connected in common to the Wire lc through the further resistors J which are preferably substantially higher in resistance than the balanced resistors K and L. It will also be noted that in the system shown in Fig. 1, there are no line or cutoff relays individual to the separate lines and in fact the only equipment individual to each line aside from the bank terminals of the line nders shown and the bank terminals of the connectors (not shown) consists of the three resistors J, K, L.

For starting one or more free line finders to Search for a calling line a common start circuit S is provided. This circuit S comprises a vacuum tube V whose anode current constantly energizes an associated relay X except when the grid of this tube V is driven negative by a potential applied to the control wire 7c. In the absence of any current received over control wire lc the grid of tube V is normally maintained at ground potential, or any other desired reference potential, by high resistance grid leak G which is connected to ground as shown, or to a bias source of any desired potential. An auxiliary relay Y of slow release type is provided and connected as shown to be operated upon the release of relay X. In the simple system shown in Fig. 1 the control wire lc is directly connected to the start wire lc' as shown.

In addition to the common start circuit S a common test circuit T generally similar to S is provided. This circuit T comprises the vacuum tube V whose anode current normally energizes relay X', and also comprises a leak G and an auxiliary relay Y controlled from relay X. The grid of tube V is connected to the test wire c of the first free line finder such as line finder I, through a common allotting device N which may be a relay chain r selecting switch and which operates in a manner well known per se to connect three wires f, c' and g of the rst idle line finder circuit to the corresponding three wires of the common test circuit as shown.

The manner of operation of the system shown in Fig. 1 is as follows: Upon the raising of the receiver at the calling station the hook switch H is closed, thus applying negative potential from the grounded exchange to the grid of tube V of the common start circuit S (over resistor L, the b wire of the line, hook switch H, the a wire of the line, resistor K, resistor J, start wire lc, i

control wire k, back contact of relay Y to the grid of tube V). The resulting decrease of anode current releases relay X, thus energizing relay Y in an obvious manner. A back contact of relay Y disconnects the grid of V, thus reener- I gizing relay X, but relay Y remains energized for an interval due to its slow release characteristics. During this energization of relay Y start magnet P of line nder I closes an obvious circuit through switch magnet M (in series with its own interruptor contacts if the switch is of step by step type, or directly if it is of power driven type), thus causing wipers W of the line finder switch MW to hunt for the calling line. If desired relay P may be omitted from the line nder of Fig. 1 or from that of Fig. 3. In such case magnet M and its interruptor if any will be directly connected in place of the relay P.

When the wipers W of the line nder switch M, W arrive at the calling line, negative potential from the grounded exchange battery is applied to the grid of tube V in common test circuit T (over resistor L. the b wire of the line, hook switch H. the a wire cf the line, resistor K, the c wire of the line, corresponding wiper W of the switch MW, the c wire of the line nder I, the common allotting device N to the grid of tube V') The resulting reduction of anode current releases relay X which causes energization of relay Y in an obvious manner. The operation of relay Y opens the circuit of relay P thus stopping switch magnet M in the line nder. Simultaneously the operation of relay Y energizes relay R in the line iinder which switches-through the a and b wires to the two windings of balanced bridge relay Q and simultaneously places ground on the c wire of the line finder and conductor n which extends to the common allotting device in order to cause this allotter to associate the test circuit T with the next idle line nder in known manner. The grounding of the c Wire by relay R in the line finder effectively removes the negative potential from the grid of tube V' since the above traced circuit for applying such negative potential to this grid is now by-passed to ground between resistors J and K (over the c wire, corresponding wiper W of switch MW, the c' wire of the line finder I, to the make contact of relay R). As a result relay X' promptly reenergizes but relay Y remains actuated for an interval due to its slow release characteristics. The allotter N should be arranged in known manner so as not to connect test circuit T to the next line finder until after relay Y has released.

In the line nder I, which is now connected to the calling line, bridge relay Q energizes over the line loop in the usual fashion, thus holding relay R over an obvious locking circuit of the latter. The subsequent operations of the equi ment beyond the line finder take place in the usual manner preferably under control of bridge relay Q.

It will be noted that now the line is balanced since resistor K is now grounded over the c wire at the end remote from the a side of the line, whereas the equal resistor L which is connected to the V side of the line is connected to the grounded exchange battery, thus providing a balanced line. The resistors K and L are thus eifectively in shunt with the windings of bridge relay Q, but since these resistors are many times larger than the impedance of the talking circuit the presence of these resistors introduces substantially no loss in the circuit. It will also be noted that no negative potential is now supplied to the start wire k' from the calling line above considered, because the intermediate point between the resistors K and J associated with this line is now grounded over the c wire as above traced. Upon release of relay Y, therefore, no negative potential will be applied to thegrid of tube V of the start circuit S until another line initiates a call.

It will also be noted that in case one of the lines shown is called the application of ground potential to the c wire of this line from the connector in the usual fashion will similarly serve to balance the line and at the same time to prevent this line from applying negative potential to the common start circuit S when its switch hook H is closed to answer the call.

It should be noted that although no negative potential is applied to start wire k by a calling line after it has been found by a line findernor by a called line after it has been selected by a connector-nevertheless, any such line will apply ground potential to this common start wire lc' through its resistor J. Such ground potential will not tend to falsely initiate a call because tube V requires a negative potential for releasing relay X. On the contrary, however, there is a possibility that the ground potential through resistor J may tend to prevent the proper initiation of another call by keeping start Wire 7c' from going suiflciently negative. For this reason resistor J is preferably made large in comparison with resistors K and L and the number of subscribers lines which are common to the start line k' is preferably maintained reasonably low.

At the same time it is advisable to make the resistance of each K and L resistor high in comparison with the impedance of the communication circuit, i. e. at least five times as high as the impedance with respect to communication frequencies of the associated subscribers line with its connected subscriber station as seen from the exchange. In fact this ratio of K or L to the communication impedance is desirably more than l and preferably of the order of 100 in order to reduce transmission losses to a negligible amount. If necessary a ratio as low as 3 may be used although this will result in a loss of almost one decibel.

Theoretically if the lines cL-b have very high K and L, 10,000 ohms for G, and 100,000 ohms for resistor J), then assuming that not more than '11% of the lines will be engaged in calling or being called at any one time, as many as D lines could be commoned together in the manner shown in Fig, l. Under such conditions a calling line would give a negative potential of more than 4% of the full exchange battery potential on the grid of tube V even if it were the eleventh line to make a call; whereas the total leakage of all lines would at most give a negative potential of 1% of the battery potential. In practice, however, the leakages of the telephone lines will often be of the order of a few megohms or tens of megohms, and thus the combined leakage of 100 such lines would, when no c wires were grounded, give a potential approaching or even exceeding the negative potential given by one calling line v in the presence of 1 0 busy lines whose c wires are grounded. While it may be possible in some cases where the resistances of the lines are unusually high to common as many as 50 or 100 lines in the simple manner shown in Fig. l, with suiiicient operating margins to give good reliability, I prefer to restrict the number of lines to be commoned together to a small number such as 2O or perferably even l0 or 5. If, therefore, the line finders are of a type serving a comparatively large group of lines such as 100 or 200 lines, I prefer to modify the arrangement of Fig. l as shown in Fig. 2.

Referring more particularly to Fig. 2, it will be seen that the lines are not all commoned to the same start wire 7c', but are commoned in groups (of which only two groups are illustrated) which are shown as each comprising three lines but which in practice may each comprise 5 or lines. The several start wires k1', 7a2', etc. of the several such groups are then associated with the one control wire k in the common start circuit S by means of a constantly operating commutatingdevice which may be an ordinary relay chain or selector switch, but which preferably is a light motor driven rotary switch or commutator adapted to run continuously for a long time without appreciable wear and designed with very light contact pressures, which are permissible in view of the high impedances and small currents associated therewith. This commutating device should complete its cycle within about one or two seconds, or preferably within a fraction of a second. Thus the start wires lc will be substantially continually connected to wire lc even though not actually connected thereto for more than a fraction of the time.

In most instances I prefer to carry this principle even further and provide a separate start wire lc for each one of the lines. In this case if the complete line group served by one group ofv line finders comprises lines the rotary commutator will be provided with 100 points. In such a system having an individual la wire per line the J resistors may be omitted.

Good reliability, however, can be secured by use of the system of Fig. 2 employing semi-common k' wires. In accordance with Fig. 2 if the system has groups of 100 lines for example, associated with one start circuit S and one group of nders, the lines will be grouped in say 10 subgroups of 10 lines each, the 10 lines of each subgroup being commoned by means of resistors and the subgroups being successively associated with the common control wire k in the manner clearly shown in Fig. 2-

Fig. 3 represents a preferred form of the common start circuit S and the common test circuit T of Fig. l. In the arrangement of Fig. 3 one single common circuit ST replaces the two common circuits S and T of Fig. l. The remainder of the system is essentially as shown in Fig. l, excepting that the line finders are slightly modied so that the battery for relay P is supplied from a back contact of relay R rather than from a common multiple associated with common start circuit S as shown in Fig. 1. The modification shown in 3 may be used with the simple system of Fig. l wherein the J resistors are actually continually connected to the wire 7c or in the preferred system (obtained by modifying Fig. l according to Fig. 2) wherein the J resistors are only substantially continually connected to the control Wire 7c.

The manner of operation of Fig. 3 is as follows: Upon the initiation of a call negative potential is received over wire k as in the case of Fig. l and this potential passes over back contacts of relays Y and Z to the grid of tube V" thus causing the release of relay X". The release of relay X energizes relay Z" over back Contact of X" and back contact of Y". The consequent operation of relay Z transfers the grid lead of tube V to the c wire of the line finder while another contact of relay Z simultaneously energizes relay P in the line nder to cause magnet M to step the wipers W around in search of the calling line. This transfer of the grid lead of tube V away from the wire lc removes the negative potential from this grid thus causing relay X to reenergize substantially instantaneously. Relay Z does not release, however, but locks up in series with relay Y to ground on the malte-before-break contact of relay X, thus also energizing relay Y. Upon the arrival of wipers l?! of the line finder at the terminals of the line negative potential is again applied to the grid of tube V, this time over the c wire of line finder and the lower front Contact of relay Z. Relay X" accordingly again releases and this time the release of relay X energizes relay R in the line finder over the back contact X, front contact Y and wire y. The locking circuit of relays Z and Y" is broken, thus releasing relay Z immediately, but relay Y remains energized for an interval because of its slow release characteristics. The release of Z causes P to release thus stopping switch MW. During the holding time of relay Y relay R is energized over back contact X, front contact Y" and wire g, and the operation of this relay R breaks the circuit of relay P (already broken by Z"), applies a ground to Wire n to cause the allotter N to connect ST to the next line nder after the release of relay Y and switches the a and b wires through to bridge relay Q so that the latter` operates in the usual manner and holds relay R. Hereafter Y" releases and the allotter transfers ST to the next line finder.

While the preferred form of my invention ernploys normally open line loops which are closed by the hook switch H to initiate a call, it is within the scope of my invention to use normally closed line loops which are opened for calling, or normally closed loops whose resistance is varied to initiate a call. In cases where the loop is opened or increased in resistance for calling the hereinabove described type of system having a separate k wire per line is preferably used and the start circuit is modified in obvious manner to initiate a call if relay X fails to release rather than if it releases.

The tubes V, V' and V" may be grid controlled gaseous discharge tubes of the trigger type instead of high vacuum tubes so as to remain conducting when once ignited. In such case a special battery with grounded negative may be used for feeding the L resistors and relays X, X and X may be correspondingly modified to operate upon the initiation of a call. Or high vacuum tubes may be used with a self-locking circuit of known type to remain either conducting or non-conducting until reset. Any of these expedients will permit a very brief contacting time for the commutating device D, thus permitting a very rapid operation of this device while still insuring operation (or release) of relay X.

If some of the lines of an exchange have leakages too high to give reliable operation with the system of the present invention such lines may be segregated and served by conventional equipment including line and cutoff relays. Or without segregating such lines, line and cutoff relays may be added thereto and instead of connecting the leaky lines directly to the start circuits of my invention the line relays may be connected to actuate such start circuits.

It should further be noted that my invention may be used in part as well as in its entirety. For example the start circuit arrangement of the invention may be used without the special test circuit of the invention. In such case the testing may be performed across the a and b wires with a simple bridged test relay such as Q, testing only lines whose c wires are ungrounded.

Although the invention has been described and illustrated in conjunction with line nders of the selector switch type, which may be either rotary or linear motion switches of step by step or power driven type, it will be understood that the invention is also applicable to relay type and cross bar type line finders although in such case the test multiples would require modication in an obvious manner in order to mark the identity of the calling line in coordinate fashion. The switches may be of the homing or non-homing type and if of the latter type may have two or more home positions to shorten the hunting time.

Instead of starting only nder for hunting all nders may be started simultaneously or if the finders have two or three home positions two or three finders may be started. Alternatively the group of lines associated with one iinder may be split and two separate start circuits associated therewith. Then if nders with two home positions are used the allotter may be arranged to start not simply the first idle iinder but rather the first idle finder which is occupying such a home position as to find the calling line most quickly` Although certain embodiments of the invention have been shown and described for purposes of illustration, it will be understood that modifications, adaptations and alterations thereof occurring to one skilled in the art may be made without departing from the scope of the invention as dened in the appended claims.

What I claim is:

l. A telephone or the like exchange system comprising a number of subscribers lines each having a first and a second conductor, a subscribers station connected to each line and including means for varying the conductance between said conductors of said line to initiate a call, a, high ohmic resistance per line each resistance being substantially non-reactive and having one end permanently connected to the rst conductor of its associated line and its other end permanently connected to a common return point, a common start circuit sufficiently sensitive to be actuated in response to the said variation of the conductance between the conductors of one of said lines even in series with the associated high resistance, said common start circuit being connected to said common return point, and means for providing connection between said common start circuit and the second conductor of each line to cause the actuation of said circuit in response to the intiation of a call comprising a common control conductor connected to said start circuit, a further high ohmic resistance per line each of said further resistances having one end permanently connected to the second conductor and its associated line and constantly operating distributor -means for connecting said common control conductor to the other ends of said further high ohmic resistances in rapid succession.

2. A telephone or the like exchange system comprising a number of subscribers lines each having a first and a second conductor, a subscribers station connected to each line and including means for varying the conductance between said conductors of said line to initiate a call, a high ohmic resistance per line each resistance being substantially non-reactive and having one end permanently connected to the rst conductor of its associated line and its other end permanently connected to a common return point, a common start circuit sufliciently sensitive to be actuated in response to the said variation of the conductance between the conductors of one of said lines even in series with the associated high resistance, said common start circuit being connected to said common return point, and means for providing connection between said common start circuit and the second conductor of each line to cause the actuation of said circuit in response to the initiation of a call comprising a common control conductor connected to said.

start circuit, a further high ohmic resistance per line each of said further resistances having one end permanently connected to the second conductor and its associated line, a plurality of semicommon start conductors each connected to the other ends of a plurality of said further high ohmic resistances, and constantly operating distributor means for connecting said common control conductor successively to said semi-common start conductors.

3. A telephone or the like communication exchange system comprising a number of subscribers lines extending to a central exchange and each having a rst and a second conductor symmetric to ground, a subscribers station connected to each line and including means for varying the conductance between said conductors of said line to initiate a call, a rst and a second high ohmic resistance of approximately equal value per line, each resistance having a value at least five times as high as the impedance with` respect to communication frequencies of its associated line with its connected station as seen from the exchange, and the rst resistance having one end permanently connected to the rst conductor of its associated line and its other end permanently connected to a common return point which is at ground potential at least with respect to communication frequencies, and the second resistance having one end permanently connected lto the se-cond conductor of its associated line, a third conductor individually associated with each line within the exchange and permanently connected to the other end of the associated second resistance, a common control conductor, a. common start circuit suiiciently sensitive to be actuated in response to the said variation of the conductance between the conductors of one of said lines even in series with both the associated high resistances said common start circuit being connected between said common return point and said common control conductor, means for providing connection between said common control conductor and the third conductor of each line to cause the actuation of said circuit in response to the initiation of a call, and means for grounding said third conductor of any line at least with respect to communication frequencies during the communication period of a call over such line, whereby said line and connected resistances are symmetric to ground during communication.

4. A telephone or the like exchange system comprising a number of subscribers lines extending to a central exchange and each having a nrst and a second conductor, a subscribers station connected to each line and including means for closing a loop connection between said conductors of said line to initiate a call, a first and a second high ohmic resistance per line each resistance having a value at least ve times as high as the impedance with respect to communication frequencies of its associated line with its connected station as seen from the exchanges, and the first resistance having one end permanently connected to the rst conductor of its associated line and its other end permanently connected to a common return point, and the second resistance having one end permanently connected to the second conductor of its associated line, a third conductor individually associated with each line within the exchange and permanently connected to the other end of the associated second resistance, a common control conductor, a common start circuit sufficiently sensitive to be actuated in response to the closed condition of said loop connection even in series with both the associated high resistances, said common start circuit being connected between said common return point and said common control conductor, means for providing connection between said common control conductor vand the third conductor of each line to cause the actuation of said circuit in response to the initiation of a call, and means for applying to said third conductor of any line during the continuance of a call over such line a fixed potential of such Value as to prevent response of said common start circuit in response to the closed condition of said loop connection.

5. A system according to .claim 4, wherein said means for providing connection between said common control conductor and the third conductor ci each line comprises constantly operating distributor means for connecting said common control conductor to the third conductors of the several lines in rapid succession.

6( A system according to claim 4, wherein said means for providing connection between said common control conductor and the third conductor of each line comprises a third high ohmic resistance per line each such third resistance having one end permanently connected to the third conductor of its associated line and its other end permanently connected to said common control conductor.

7. A system according to claim 4, wherein said means for providing connection between said common control conductor and the third conductor of each line comprises a third high ohmic resistance per line each such third resistance having one end permanently connected to the third conductor of its associated line, a plurality of semi-common start conductors each connected to the other ends .of a plurality ofsaid third resistances, and constantly operating distributor means for connecting said common control conductor successively to said semi-common start conductors.

8. A telephone or the like exchange system comprising a number of subscribers lines extending to a central exchange and each having a rst and a second conductor, a subscribers statio-n connected toieach line and including means for closing a loop connection between said conductors of said line to initiate a call, a rst and a second high ohmic resistance per line each resistance having a value at least ve times as high as the impedance with respect to communication frequencies of its associated line With its connected station as seen from the exchanges, and the rst resistance having one end permanently connected to the rst conductor of its associated line and its other end permanently connected to a common return point, and the second resistance having one end permanently connected to the seco-nd conductor of its associated line, a third conductor individually associated with each line within the exchange and permanently connected to the other end of the associated second resistance, a common start circuit suiciently sensitive to be actuated in response to the closed condition of said loop connectlon even in series with both the associated high resistances said common start circuit being connected to said common return point, a third high ohmic resistance per line each such third resistance having one end permanently yconnected to the third conductor of its associated line, a plurality of semi-common start conductors each connected to the other ends of a plurality of said third resistances, means for providing connection between said common start circuit and each of said semi-common start conductors to cause the actuation of said start circuit in response to the initiation of a call, and means for applying to said third conductor of any line during the continuance of a call over such line a Xed potential cf such value as to prevent actuation of said common start circuit in response to the closed condition of said loop connection.

9. A system according to claim 4, wherein said common start circuit comprises electron discharge means and relay means actuated thereby.

10. A system according to claim 4, further comprising a test circuit suiciently sensitive to be actuated in response to the closed condition of said loop connection even in series with both the associated high ohmic resistances said start circuit being connected to said common return point, normally unoperating search means for connecting said test circuit successively to said third conductors of the lines, means for starting said search means into operation in response to the actuation of said common start circuit, and means for stopping said search means in response to the actuation of said test circuit.

11. A system according to claim 4, further comprising a common test circuit suiciently sensitive to be actuated in response to the closed condition of said loop 'connection even in series with both the associated high ohmic resistances said start circuit being connected to said common return point, a plurality of normally unoperating line iinder means for connecting said test circuit successively to said third conductors of the lines, means for starting one of said line iinder means into operation in response to the actuation of said common start circuit, means for associating said one of said line finder means with said common test circuit, and means for stopping said line nder means in response to the actuation of said common test circuit.

12. A system according to claim 4, further comprising a common test circuit suciently sensitive to be actuated in response to the closed condition of said loop connection even in series with both the associated high ohmic resistances said start circuit and said test circuit jointly comprising a common electron discharge device and said start circuit being connected to said common return point, a plurality of normally unoperating line nder means for connecting said test circuit successively to said third conductors of the lines, means for starting one of said line nder means into operation in response to the actuation of said common start circuit, means for associating said one of said line finder means With said common test circuit, and means for stopping said line finder means in response to the actuation of said common test circuit.

13. A telephone exchange system according to claim 3, wherein each of said first and second high ohmic resistances has sufcient resistance to cause substantially no impairment of the transmission of speech nor of any auxiliary signals of alternating and direct current types which are customarily transmitted over telephone Wires.

14. A telephone exchange system according to claim 4, wherein each of said rst and second high ohmic resistances has a value of at least 10,000 ohms.

GERALD DEAKIN. 

